The kinematics of galaxies may be investigated by means of the motion of
their stars or
gas. In BCGs the former is in general not possible, due to the absence
of strong absorption
lines, and studies have been restricted to the gas phases.

Chamaraux et al. (1970)
were the first to detect neutral hydrogen in a BCG, namely
IIZw40, and more BCGs were detected in various
surveys (not only targeting BCGs) :
Lauqué (1973),
Bottinelli et al. (1973,
1975),
Chamaraux (1977).
Gordon and Gottesman
(1981) and
Thuan and Martin
(1981)
conducted the first extensive
systematic surveys of neutral hydrogen in BCGs, and in total more than
200 BCGs,
predominantly in the northern hemisphere, were observed and the majority
detected. BCGs have been found to be gas rich.
The ratio of neutral hydrogen mass to integrated blue luminosity is
typically in the
range 0.1 MHI /
LB 1.0 (in solar
units, Thuan and
Martin 1981,
Gordon and Gottesman 1980).
Thus BCGs are as gas rich as spirals and dIs, but less than LSBGs
(Staveley-Smith et
al. 1992).

There is a current view suggesting that the formation of stars depends
primarily on the amount of molecular gas. However the situation in low
metallicity gas is still under debate. Many attempts to detect CO in BCGs
galaxies have been reported so far
(Combes 1986,
Young et al. 1986,
Arnault et al. 1988,
Sage et al. 1992,
Israel et al. 1995,
Gondhalekar et
al. 1998)
but the CO luminosity of BCGs is very low, in comparison with their observed
star formation rate, mostly yielding only upper limits. This lack of
detection may be because the low metallicity of BCGs hides the true
molecular phase by
a low CO to H2 conversion factor. However other explanations
may be invoked as well:
the CO excitation could be lower than for molecular clouds in our Galaxy, or
the molecular clouds in BCGs could be UV-photodissociated as a result of
high star formation rates.
Gondhalekar et
al. (1998)
conclude that
the CO luminosity correlates rather weakly with the FIR luminosity, i.e. FIR
luminosity may not be a good tracer of molecular gas.
Obviously the lack of CO detection does not preclude the
presence of H2 molecules in these gas-rich galaxies.
In fact there are mechanisms by
which molecular hydrogen can be formed in absence of grains from hydrogen atoms
in gaseous phase via a reaction involving negative hydrogen ions
(Lequeux and
Viallefond 1980).
It is therefore possible that in star-forming galaxies with well localised
massive star formation surrounded by huge H I gaseous envelopes that the
molecular hydrogen is abundant and makes up a significant fraction of the dark
matter dynamically detected
(Lequeux and
Viallefond 1980,
Lo et al. 1993).
New capabilities such as the FUSE mission
will offer the unique possibility to detect for the
first time cold H2 in absorption against the stellar continuum of
blue massive
stellar clusters. IZw18 will be the first target to be searched for
H2.

Östlin et al.
(1999a,
b)
investigated the H velocity fields of a sample of
luminous BCGs utilising scanning Fabry-Perot interferometry. The
velocity fields were
found to be complex, and in many cases showed evidence for dynamically
distinct components,
e.g. counter rotating features. Their analysis suggests that mergers
involving gas rich dwarfs
are the best explanations for the starbursts in these systems. Masses
were modelled
both dynamically and photometrically, and some galaxies showed apparent
rotational mass
deficiencies which could be explained if the studied BCGs are not
primarily supported by rotation, if stars and gas are dynamically decoupled
(e.g. due to gas flows) or if the galaxies are not in dynamical equilibrium.
There are also indications that the width of emission lines in BCGs is
related to virial
motions and may provide dynamical mass estimates (see
Sect. 7.1, and
Melnick et al. 1987).

Flows in the ionised gas have been detected in several BCGs
(Marlowe et al. 1995;
Martin 1996,
1998;
Meurer et al. 1997),
and suggested by X-ray observations in
VIIZw403
(Papaderos et
al. 1994).
Flows have also been found from studies of the Ly emission.
Although Ly emission in
starbursts is expected to be strong, it turns out that dust
is very effective in suppressing this line because the effects of
resonant scattering in
a gas-rich medium dramatically reduce the effective mean free path of
the Ly photons.
On the other hand this mechanism does not explain why in
many galaxies with little dust content such as IZw18
(Kunth et al. 1994)
Ly
is seen in absorption whereas in dustier ones such as Haro2
(Lequeux et al. 1995)
the line is seen in emission but with a clear P-Cygni profile.
Kunth et al. (1998)
found that the
strength of Ly emission is in
fact only weakly correlated with metallicity and suggested that
the dynamical state of ISM is also a major regulating mechanism. A new
model explains Ly
profiles in starburst galaxies by the hydrodynamics of superbubbles
powered by massive stars
(Tenorio-Tagle et
al. 1999).